In recent years, vehicle detection apparatuses for detecting a vehicle traveling in the same lane as a subject vehicle based on a captured image of a surrounding road have been developed. For example, U.S. Pat. No. 5,487,116 discloses a conventional vehicle detection apparatus that first extracts white boundary lines of a vehicular lane where the subject vehicle is traveling (a subject lane) from an image captured by a CCD camera to create an edge image by differential calculus processing for detecting lane width. The apparatus then determines if there is a preceding vehicle in the same lane as the subject vehicle by extrapolating image data based on the lane width of the subject lane.
However, as the vehicle detection apparatus described above uses a CCD captured image to determine the subject lane and an adjacent lane, it is impossible to detect an adjacent lane when the white boundary line between the subject lane and the adjacent lane is hidden by another vehicle. It is also a problem of the conventional lane detection apparatus that it cannot determine if the adjacent lane is an oncoming lane, a passing lane or the like. That is, a traveling direction of the adjacent lane cannot be detected by the conventional apparatus.